DURING the past two weeks, the United States Supreme Court has fundamentally expanded the scope of religion in public life.

First, the justices ruled that a New York school district could not close its doors to religious groups if it allowed other organizations to use its facilities after-hours. Then the justices refused to hear a challenge to a Texas court decision that students could lead graduation prayers at a public high school. Next, the court unanimously declared that Hialeah, Fla., could not ban the sacrifice of animals by adherents of the Santeria faith. Finally, the court ruled 5 to 4 on Friday that an Arizona schoo l district could be required under federal law to pay for a sign-language interpreter for a deaf student attending a parochial high school.

The impact of the recent rulings will not be known until lower courts and legislatures interpret them in coming years. For example, it is not clear how the decisions will affect voucher programs that pay for students to attend parochial schools. But the signal the court has sent is unmistakable: Religious people must not be denied rights or privileges available to nonbelievers.

"I think clearly the court has turned a corner on religious freedom and religion in public life," says Jim Henderson, an attorney for the conservative American Center for Law and Justice.

Mr. Henderson says that the court rulings will affect a slew of cases that come across his desk every day. In one case, a religious group was not allowed to use a government building after-hours to hold a prayer meeting. In another instance, a high school student was not allowed to display a religious message on a bulletin board that other students could use as they liked. After the Supreme Court's recent rulings, Henderson believes, those bans are now unconstitutional.

Liberal groups are dismayed by this development. Barry Lynn, executive director of Americans United for Separation of Church and State, called Friday's ruling "a very bad decision" and said it "is probably the first time in US history that the taxpayers' money has been used to subsidize religious indoctrination."

At the same time, however, Mr. Lynn sought to minimize the ruling's impact. "It's a very narrowly worded decision," he said. "It doesn't appear to open the door for vouchers or other direct parochial-school aid."

The case decided Friday began when the parents of James Zobrest, a deaf student, enrolled him in a Roman Catholic high school in Tucson, Ariz. The Zobrests asked the local school board to supply their son with a sign-language interpreter under the federal Individuals with Disabilities Education Act. The board refused, arguing that paying for an interpreter would violate the First Amendment's prohibition against establishment of religion. The Zobrests sued the school district, citing another clause of the

First Amendment that bars the government from interfering with the free exercise of religion. The lower courts sided with the school district, but a majority of the high court disagreed.

Chief Justice William Rehnquist, in the majority opinion, wrote, "We have consistently held that government programs that neutrally provide benefits to a broad class of citizens defined without reference to religion are not readily subject to an Establishment Clause challenge just because sectarian institutions may also receive an attenuated financial benefit."

Justice Harry Blackmun, joined by Justice David Souter, wrote a blistering dissent in which he accused the majority of straying "from the course set by nearly five decades of Establishment Clause jurisprudence." Justices Sandra Day O'Connor and John Paul Stevens dissented on the grounds that the court should not have tackled the constitutional issue at all.

The Zobrest ruling and the other recent decisions leave many constitutional scholars more than a little mystified because they do not establish any clear standard by which to judge future cases. The reigning standard is the 1971 Lemon v. Kurtzman, which establishes a three-part test to determine if a government practice violates the Establishment Clause. But the Lemon standard has not been consistently applied. In Zobrest, the court majority did not invoke Lemon, nor did justices overturn it and establis h a new standard.

Church-state jurisprudence "was a muddle before and it's a muddle now," says Prof. Michael McConnell of the University of Chicago Law School.

Jesse Choper, a constitutional scholar at the University of California at Berkeley, attributes the court's indecision to Justice Byron White. Mr. White opposes Lemon, but Professor Choper speculates that he was unwilling to create a new standard because "he has one foot out the door."

As a result, it will be up to Ruth Bader Ginsburg, if she is confirmed to the court, to steer a new course on church-state relations. Choper believes this is the area where Judge Ginsburg would have the greatest impact. "I think she'll be a stronger separationist than White," he says.